Ask an expert: Servo subwoofers; Genesis speakers – and more

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Ask an expert

Gentlemen – what can you tell me about Genesis speakers and servo subwoofers please?

Paul McGowan writes as follows: When Arnie Nudell and I ran Genesis loudspeakers in the 1990′s a big part of the company’s story was built in servo subwoofers; something both Arnie and I were passionate about (still are).  The way we divided the company’s design duties up was I handled the electronics and Arnie did everything else.

Servo subwoofers present a unique design challenge to whomever designs their electronics; in this case me.  Aside from all the challenges presented by the servo circuitry itself, there’s the issue of overload and clipping.  Clipping the subwoofer in a servo setup is nothing short of nasty and, if bad enough, can send a woofer into a death spiral.

Standard practice had always been to add a compressor or limiting circuit on the subwoofer’s input (still is today).  This simple circuit was like an automatic volume control – if the incoming sound got too loud, the volume of the sub turned down to compensate, thus reducing the chance for clipping (clipping sounds like a bad case of gas).

Problem was (and still is) adding a compressor to the circuit made the sub sound wimpy because you had to really put on the brakes hard.  What we needed was a way to know when the sub amp had run out of steam and was about to clip – not a guess as to how loud and at what frequency this would occur at. The solution turned out to be simple – but only because we stopped trying to make what everyone else was doing better.

We knew that just before the amp clipped the power supply voltages dropped because we were delivering too many watts.  So we designed a circuit that monitored the power supply, NOT the incoming audio.  That way, regardless of what the bass notes were, the subs thundered along mightily until the power supply of the amp just couldn’t give any more juice and then, and only then, we lowered the signal level to compensate.  It worked perfectly.

I bring this story to light because maybe, just maybe, some designer out there is struggling with a problem and this might help him or her understand it helps a lot to stop focusing on making what every body else is doing better and going at it alone with a fresh look.

What every body else is doing isn’t going to help you create something new and wonderful.

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